1. Field of the Invention
The invention relates to an implantable arrangement for mechanical coupling of an output-side driver member of an active or passive hearing system, the driver member being adapted to be excited to mechanical vibrations, to a preselected coupling site on the ossicular chain, the footplate of the stapes or a membrane which closes the round window or an artificial window in the cochlea, in the vestibulum or in the labyrinth (equilibrium organ), via a coupling arrangement which has a coupling rod which can be excited to mechanical vibrations by the driver member, and a coupling element which can be connected to said preselected coupling site, the coupling rod and the coupling element being interconnected via at least one coupling and at least a section of the coupling element which in the implanted state contacts the coupling site being designed for vibratory input to the coupling site.
2. Description of Related Art
Partially implantable or fully implantable active hearing systems for direct mechanical stimulation are known. In these hearing systems the acoustic signal is converted into an electrical signal by a converter (microphone) and is amplified in an electronic signal processing unit; this amplified electrical signal is supplied to an implanted electromechanical converter the output-side mechanical vibrations of which are supplied directly, i.e. with direct mechanical contact, to the middle ear or inner ear. This applies regardless of whether pure labyrinthine deafness with a completely intact middle ear or combined deafness (middle ear and inner ear damaged) is to be rehabilitated. Therefore, implantable electromechanical converters and processes for direct coupling of the mechanical converter vibrations to the intact middle ear or to the inner ear for rehabilitation of pure labyrinthine deafness and also to the remaining ossicles of the middle ear in an artificially or pathologically altered middle ear for treatment of conductive deafness and their combinations have been described in the more recent scientific and patent literature.
Basically all physical conversion principles can be used as electromechanical converter processes, such electromagnetic, electrodynamic, magnetostrictive, dielectric, and piezoelectric. In recent years various research groups have focused essentially on two of these processes: electromagnetic and piezoelectric. An outline of these converter versions can be found in Zenner and Leysieffer (HNO 1997, Vol. 45, pp. 749 -774).
In the piezoelectric process, mechanically direct coupling of the output-side converter vibrations to the middle ear ossicle or directly to the oval window is necessary. In the electromagnetic principle, the force coupling, on the one hand, can take place via an air gap (xe2x80x9ccontactlessxe2x80x9d), i.e. only a permanent magnet is placed by permanent fixation in direct mechanical contact with a middle ear ossicle. On the other hand, it is possible to dispose the entire converter within a housing (the coil and the magnet being coupled with the smallest possible air gap) and to transfer the output-side vibrations via a mechanically stiff coupling element with direct contact to the middle ear ossicle (Leysieffer et al., HNO 1997, Vol. 45., pp. 792-800).
The patent literature contains some of the aforementioned versions of both electromagnetic and also piezoelectric hearing aid converters: U.S. Pat. No. 5,707,338 (Adams et al.), WO 98/06235 (Adams et al.), WO 98/06238 (Adams et al.), WO 98/06236 (Kroll et al.), WO 98/06237 (Bushek et al.), U.S. Pat. No. 5,554,096 (Ball), U.S. Pat. No. 3,712,962 (Epley), U.S. Pat. No. 3,870,832 (Fredrickson), U.S. Pat. No. 5,277,694 (Leysieffer et al.), published European Patent Application Nos. EP-A-0 984 663 and EP-A-0 984 665 (corresponding to commonly owned U.S. Patent Application Nos. 09/275,872 and 09/311,563, respectively) (Leysieffer), U.S. Pat. No. 5,015,224 (Maniglia), U.S. Pat. No. 3,882,285 (Nunley), and U.S. Pat. No. 4,850,962 (Schaefer).
The partially implantable piezoelectric hearing system of the Japanese group of Suzuki and Yanigahara presupposes for implantation of the converter the absence of the middle ear ossicles and an empty tympanic cavity in order to be able to couple the piezoelement to the stapes (Yanigahara et al.: Efficacy of the partially implantable middle ear implant in middle and inner ear disorders, Adv. Audiol., Vol. 4, Karger Basel (1988), pp. 149-159; Suzuki et al.: Implantation of partially implantable middle ear implant and the indication, Adv. Audiol., Vol. 4, Karger Basel (1988), pp. 160166). Similarly, in the process of an implantable hearing system for those suffering from labyrinthine deafness in accordance with U.S. Pat. No. 4,850,962 (Schaefer), basically, the incus is removed in order to be able to couple a piezoelectric converter element to the stapes. This also applies especially to other developments which are based on the Schaefer technology and which are documented in the aforementioned patents (U.S. Pat. No. 5,707,338, WO 98/06235, WO 98/06238, WO 98/06236, and WO 98/06237).
Conversely, the electromagnetic converter of BALL (xe2x80x9cFloating Mass Transducer FMTxe2x80x9d, U.S. Pat. No. 5,624,376, and U.S. Pat. No. 5,554,096) is fixed with titanium clips directly to the long process of the incus when the middle ear is intact. The electromagnetic converter of the partially implantable system of FREDRICKSON (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107-121) is mechanically coupled directly to the body of the incus when the ossicular chain of the middle ear is likewise intact. The same applies to the piezoelectric and electromagnetic converters of LEYSIEFFER (Leysieffer et al.: An implantable piezoelectric hearing aid converter for patients with labyrinthine deafness, HNO 1997/45, pp. 792-800; U.S. Pat. No. 5,277,694, U.S. Patent Application Nos. 09/275,872 and 09/311,563 (Leysieffer)). Also, in the electromagnetic converter system of MANIGLIA (Maniglia et al: Contactless semi-implantable electromagnetic middle ear device for the treatment of sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 121-141), when the ossicular chain, is intact, a permanent magnet is permanently fixed mechanically to the ossicular chain but is, however, mechanically driven via an air gap coupling by a coil.
In the described converter and coupling versions, basically, two implantation principles can be distinguished:
a) On the one hand, the electromechanical converter with its active converter element is located itself in the middle ear region in the tympanic cavity and the converter is directly connected there to an ossicle or the inner ear (U.S. Patent No. 4,850,962, U.S. Pat. No. 5,015,225, U.S. Pat. No. 5,707,338, WO 98/06235, WO 98/06238, WO 98/06236, WO 98/06237, U.S. Pat. No. 5,624,376, and U.S. Patent No. 5,554,096).
b) On the other hand, the electromagnetic converter with its active converter element is located outside of the middle ear region in an artificially formed mastoid cavity. The output-side mechanical vibrations are then transmitted to the middle or inner ear by means of mechanically passive coupling elements via suitable surgical accesses (the natural aditus ad antrum, opening of the chorda-facialis angle or via an artificial hole from the mastoid) (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107-121; U.S. Pat. No. 5,277,694; U.S. patent application Ser. Nos. 09/275,872 and 09/311,563 (Leysieffer)).
In a)-type versions, the converter can be made as a so-called xe2x80x9cfloating massxe2x80x9dconverter, i.e. the converter element does not require any xe2x80x9creactionxe2x80x9d,via secure screwing to the skull bone, rather it vibrates based on the laws of mass inertia with its converter housing and transmits these vibrations directly to a middle ear ossicle (U.S. Pat. No. 5,624,376, U.S. Pat. No. 5,554,096, U.S. Pat. No. 5,707,338, and WO 98/06236). On the one hand, this means that an implantable fixation system on the cranial vault can be advantageously omitted, and, on the other hand, this version disadvantageously means that bulky artificial elements must be placed in the tympanic cavity, and their long-term stability and biostability are currently not known or guaranteed, especially in the case of temporary pathological changes of the middle ear (for example, otitis media). Another major disadvantage is that the converter together with its electrical supply line has to be transferred from the mastoid into the middle ear and must be fixed there using suitable surgical tools; this requires expanded access through the chorda facialis angle and, thus, entails a latent hazard to the facial nerve which is located in the immediate vicinity.
In the b)-type converter versions, the converter housing with the implantable positioning and fixation systems is attached to the cranial vault (advantageous embodiment U.S. Pat. No. 5,788,711). Both in the partially implantable system of FREDRICKSON (Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107-121), as well as in the fully implantable hearing system of LEYSIEFFER and ZENNER (HNO 1998, vol. 46, pp. 853-863 and 844-852), when the vibrating driver member is coupled to the body of the incus, it is assumed, for permanent and mechanically secure vibration transmission, that the tip of the coupling rod, which is placed in the laser-induced depression of the middle ear ossicle, undergoes osseointegration over the long term, i.e. the coupling rod coalesces solidly with the ossicle, and thus, ensures reliable transmission of dynamic compressive and tensile forces. This long-term effect, however, is currently not yet scientifically proven or certain. Furthermore, in this type of coupling, in case of a technical converter defect, there is the disadvantage that decoupling from the ossicle to remove the converter can only be done with mechanically based surgical methods; w this can mean considerable hazard to the middle ear and especially the inner ear.
The major advantage of these converter embodiments as per b) however, is that the middle ear remains largely free and coupling access to the middle ear can take place without major possible hazard to the facial nerve. One preferable surgical process for this purpose is described in U.S. Pat. No. 6,077,215. Basic advantageous forms of passive coupling elements for transmission of the output-side converter vibrations from the mastoid to the middle ear or inner ear are described in U.S. Pat. No. 5,277,694; U.S. Pat. No. 5,941,814; and in HNO 1998 Vol. 46, pp. 27-37xe2x80x94Lehner et al.: xe2x80x9cCold-flowing elements for coupling of an implantable hearing aid converter to the auditory ossicle or perilymphxe2x80x9d. The coupling elements are especially made of gold, preferably, soft-annealed fme gold, in the form of a C-band for the long process of the incus, a band loop for the long process of the incus and a tiny bell for the head of the stapes, and these coupling elements can be coupled using instruments which are standard in ear surgery, and if necessary, they can also be detached again.
Commonly owned U.S. Patent Application No. 09/626,745 (filed on Jul. 26, 2000 and entitled xe2x80x9cArrangement for Mechanical Coupling of a Driver to a Coupling Site of the Ossicular Chainxe2x80x9d) describes an implantable arrangement for mechanical coupling of an output-side driver member of an active or passive hearing system, the driver member being adapted to be excited to mechanical vibrations to a preselected coupling site on the ossicular chain, the footplate of the stapes or a membrane which closes the round window or an artificial window in the cochlea, in the vestibulum or in the labyrinth (equilibrium organ), via a coupling arrangement which has a coupling element which can be connected to the preselected coupling site. An attenuator element with entropy-elastic properties which, in the implanted state, contacts the coupling site, causes a coupling with low characteristic acoustic impedance and a reduction of the risk of damage to natural structures in the area of the coupling site during and after implantation.
WO 99/08475 discloses an active hearing system in which a capacitive sensor converts vibrations of the malleus into an electrical signal which after passing through an electronic circuit is supplied to a stimulator, which for its part, mechanically or electrically stimulates the inner ear. The capacitive sensor includes a first electrode, which is pivotally coupled to the malleus via a ball joint coupling, and a second electrode, which is either rigidly fixed to the mastoid or is likewise pivotally coupled to the mastoid via a ball joint coupling. The ball joint coupling is designed such that the two electrodes can freely align themselves with respect to one another even if the vibration direction of the malleus changes for example as a function of frequency.
An arrangement is described in U.S. Pat. No. 5,941,814 in which the first coupling half is essentially rod-shaped and the second coupling half is made roughly sleeve-shaped, and by pushing and/or turning the two coupling halves, the relative location of the coupling rod and coupling element can be adjusted in situ at the implantation site. The two components are fixed reliably with long term stability in the set relative position by applying a crimping force, using a crimping tool, to the sleeve-shaped second coupling half, by which the latter is plastically cold-formed, whereas the rod-shaped first coupling half is not subjected to plastic cold-forming under the action of a crimping force.
In addition to the described active hearing systems, passive hearing systems are also known in the form of prostheses as total replacement (T.O.R.P.=total ossicular replacement prosthesis) or as partial replacement (P.O.R.P.=partial ossicular replacement prosthesis) for the ossicular chain (D.I. Bojrab et al. xe2x80x9cOssiculoplasty with composite prosthesesxe2x80x9d,in Otolaryngologic Clinics of North America, Vol. 27, No. 4, 1994, pp. 759-776). In these passive systems the eardrum itself or an area of the still intact xe2x80x9cremainderxe2x80x9d,of the ossicular chain facing the eardrum forms the output-side driver member. Thus, U.S. Pat. No. 5,370,689 discloses as a stapes replacement a passive middle ear prosthesis which comprises an elongated rod section one end of which is connected to the footplate of the stapes. An eyelet is provided at the other end of the rod section and is pushed over the free end of the long process of the incus. The motion of the stapes replacement which is driven by the long process of the incus is modified by a hitching member which is engaged by the stapedial tendon. For this reason the hitching member is slipped onto the rod section, the fit between the rod section and the inside surface of the hitching member being chosen such that the two parts can be moved relative to one another during implantation, whereas unwanted axial or rotational motion of the hitching member after implantation is precluded.
It is an object of this invention to provide for an arrangement which makes it possible to adjust the relative position of the two coupling halves of the coupling at the implantation site in situ as sensitively as possible in many degrees of freedom, the set relative position after implantation being reliably preserved in a simple manner with long term stability.
In conformity with the invention the arrangement includes a first coupling half of the coupling that has an outside contour with at least approximately the shape of a spherical cap which is adapted to be received in an inside contour of a second coupling half, with this inside contour being at least partially complementary to the said outside contour, wherein the coupling is adapted to be reversibly swiveled and/or turned against friction forces, but is essentially rigid with respect to dynamic forces which occur in the implanted state.
This arrangement provides an especially simple and nevertheless reliable manner that allows for moving the two coupling halves during implantation into a desired relative position. After implantation the mechanical vibrations which are induced in the first or second coupling half and which originate from the driver part are transmitted essentially rigidly to the other coupling half without the need for any additional operational step for this purpose. Proceeding from the stipulated known dynamic forces which must be transmitted in the implanted state by the coupling and from the higher forces which are typically applied by the surgeon in the course of implantation, the parameters which significantly influence the properties of the pair of the two coupling halves, such as the material, surface roughness (microgeometry) and fit (macrogeometry) are chosen such that especially the stick-slip effect and forces of friction between the coupling halves allow an easy, statically reversible adjustment of the coupling during implantation under the influence of the forces applied by the surgeon, whereas the coupling is rigid with respect to the dynamic forces to be transmitted in the implanted state.
The handling of the arrangement can be greatly simplified if the coupling is designed for reversible coupling and decoupling.
The second coupling half of the coupling can have at least two spring arms by which the first coupling half can be at least partially encompassed. The spring arms which can be connected by a material connection, for example soldering, brazing, welding, or the like, or which also can be made in one piece, can preferably contact the first coupling half with inwardly directed spring bias.
Furthermore, the second coupling half of the coupling can also have approximately a bell shape and can include especially several slots which extend essentially perpendicular to the peripheral direction and which extend to a face of the second coupling half facing the first coupling half. In this way, the first coupling half can be reliably held in the second coupling half At the same time, sufficient flexibility of the second coupling half for reversible coupling and decoupling is provided for.
Another advantageous embodiment of the invention has a second coupling which can be reversibly moved linearly and/or rotationally against friction forces, but is essentially rigid under the dynamic forces which occur in the implanted state. The first coupling half has an outside contour with an at least approximately cylindrical, preferably circularly cylindrical, shape which can be accommodated in an inside contour of the second coupling half, a contour which is at least partially complementary to the outside contour. The second coupling is preferably designed for reversible coupling and decoupling and can be positioned both between the coupling in which the first coupling half has approximately the shape of a spherical cap (first coupling) and the driver member and also between the first coupling and the coupling site. It is preferred that in the implanted state transmission of dynamic forces between the two coupling halves of the second coupling takes place essentially in the direction of the longitudinal axis of the first coupling half
An especially simple structure arises when the second coupling half of the second coupling is made as a sleeve. The sleeve can have at least one slot which runs essentially in its longitudinal direction and which extends at least over a part of the sleeve length. Furthermore, to increase the flexibility, at least one slot can extend to a face of the sleeve facing the first coupling half.
If the slot extends over the entire length of the sleeve, the wall in the region of the two edges of the slot can be formed to point outwardly and the wall can defme an insertion section into which the first coupling half can be inserted essentially perpendicular to its longitudinal axis.
At least one slot can end at least on one side in a relief opening which increases the elasticity of the second coupling half and its safety against damage, and which has a boundary line which connects the two sides of the slot, the relief opening transversely to the slot direction having a dimension which is greater than that of the slot.
The boundary line of at least one relief opening can connect the sides of the slot in an arc, especially essentially in a circular arc, or can be made in the form of a transversal slot which runs essentially perpendicular to the slot.
In another embodiment of the invention, at least one section of the wall of the sleeve of the second coupling is adapted to contact the first coupling half in an inwardly spring-biased manner. Furthermore, there can be at least two slots, and at least one section of a wall of the sleeve located between two adjacent slots is adapted to contact the first coupling half in an inwardly spring-biased manner. In doing so, it can be provided that at least two adjacent slots are connected to one another on the end side thereof, especially essentially in a U-shape manner, so that a spring tongue is formed.
To facilitate the coupling and decoupling process, the outside contour of the first coupling half of the second coupling in the area of its end facing the second coupling half can be provided with an insertion area which tapers in the direction towards the end.
For this purpose the inside contour of the second coupling half of at least one coupling in the area of its end facing the first coupling half can also be provided with an insertion area which widens in the direction towards the end. This applies both to the first and also the second coupling.
Moreover, at least a first and/or a second coupling half of at least one coupling can be advantageously connected integrally to the associated coupling element or the associated coupling rod.
The arrangement of the invention can be part of an active, partially implantable or fully implantable hearing system in which the output-side driver member is a vibratory member, especially a vibratory membrane, of an electromechanical hearing aid converter. The arrangement of the invention can however also be part of a passive hearing system, especially a partial or full middle ear prosthesis in which in the implanted state the eardrum is used as the output-side driver member.